Nitrous oxide emission related to ammonia-oxidizing bacteria and mitigation options from N fertilization in a tropical soil

Abstract

Nitrous oxide (N2O) from nitrogen fertilizers applied to sugarcane has high environmental impact on ethanol production. This study aimed to determine the main microbial processes responsible for the N2O emissions from soil fertilized with different N sources, to identify options to mitigate N2O emissions, and to determine the impacts of the N sources on the soil microbiome. In a field experiment, nitrogen was applied as calcium nitrate, urea, urea with dicyandiamide or 3,4 dimethylpyrazone phosphate nitrification inhibitors (NIs), and urea coated with polymer and sulfur (PSCU). Urea caused the highest N2O emissions (1.7% of N applied) and PSCU did not reduce cumulative N2O emissions compared to urea. NIs reduced N2O emissions (95%) compared to urea and had emissions comparable to those of the control (no N). Similarly, calcium nitrate resulted in very low N2O emissions. Interestingly, N2O emissions were significantly correlated only with bacterial amoA, but not with denitrification gene (nirK, nirS, nosZ) abundances, suggesting that ammonia-oxidizing bacteria, via the nitrification pathway, were the main contributors to N2O emissions. Moreover, the treatments had little effect on microbial composition or diversity. We suggest nitrate-based fertilizers or the addition of NIs in NH4+-N based fertilizers as viable options for reducing N2O emissions in tropical soils and lessening the environmental impact of biofuel produced from sugarcane.

Nitrification inhibitors effectively target N2O‐producing Nitrosospira spp. in tropical soil

“…From our previous work, we found that bacterial amoA (AOB) but not archaeal amoA (AOA) nor denitrification gene copy numbers (nirK, nirS) were correlated with nitrous oxide emissions from tropical soil growing sugarcane (Soares et al, 2016). Here, we found evidence that the AOB responsible for the N 2 O emissions was most phylogenetically similar to the Nitrosospira spp.…”

“…Further, the nitrite oxidizer bacteria Nitrobacter and Nitrospira have optimal growth under higher and lower nitrite supplies, respectively, which is linked to their ecological niches (Attard et al, 2010;Nowka et al, 2015). Nitrification is doubly implicated in N 2 O production, either directly or indirectly by producing NO 3 − as the basis for denitrification, and has been shown to be the main process involved in N 2 O emissions in some Brazilian sugarcane soils (Liu et al, 2016;Soares et al, 2016;Wu et al, 2017aWu et al, , 2017bLourenço et al, 2018aLourenço et al, , 2018b. The addition of nitrification inhibitors with nitrogen fertilizers is currently being explored as a sustainable management practice in Brazilian sugarcane Soares et al, 2015Soares et al, , 2016.…”

“…In agriculture, dicyandiamide (DCD) and 3,4-dimethylpyrazole phosphate (DMPP) are commercially-used nitrification inhibitors which are thought to be Cu-chelating agents acting on ammonia monooxygenase (Morales et al, 2015). These inhibitors have been shown to effectively reduce N 2 O emissions by 40%-95% in temperate and tropical soils (Misselbrook et al, 2014;Gilsanz et al, 2016;Soares et al, 2016).The effects of DCD and DMPP are generally shown to act on ammonia oxidizing bacterial abundances, perhaps because this group increases with increasing N fertilization and likely contributes to the N 2 O emissions under N fertilization in these studies (Morales et al, 2015;Soares et al, 2016). Beyond lowering N 2 O emissions, nitrogen fertilization with nitrification inhibitors might have complex effects on ammonia and nitrite oxidizer distributions (Stempfhuber et al, 2016).…”

“…Beyond lowering N 2 O emissions, nitrogen fertilization with nitrification inhibitors might have complex effects on ammonia and nitrite oxidizer distributions (Stempfhuber et al, 2016). Here, our objectives were to identify the AOB species linked to N 2 O emissions in our previous experiment (Soares et al, 2016) and to compare the effects of urea fertilization with or without nitrification inhibitors on amoAcontaining nitrifier abundances. Here, our objectives were to identify the AOB species linked to N 2 O emissions in our previous experiment (Soares et al, 2016) and to compare the effects of urea fertilization with or without nitrification inhibitors on amoAcontaining nitrifier abundances.…”

“…It is yet unknown which nitrifiers are specifically affected by nitrogen fertilization with the nitrification inhibitors DCD and DMPP, especially in tropical conditions. To gain insight into the environmental niches of different nitrifiers, wee included the previously generated 16S rRNA gene, nitrification and denitrification gene copy numbers and soil environmental variable datasets (Soares et al, 2016). We sequenced amoA AOB amplicons and mined the previous 16S rRNA amplicons from a 258 day field experiment encompassing treatments with urea and two nitrification inhibitors, DCD and DMPP, on soils growing ratoon sugarcane.…”